Carboniferous biogenic sedimentary structures on the northwestern margin of Jungar Basin

Volcanic clastic rocks of 2 300 m thick are developed in the Carboniferous of the Halaalate Mountains in the northwestern margin of the Jungar Basin. The research of sedimentology indicates that they were formed by the sedimentation of deep-water environnent. They could be divided into three ichnofacies from the lower part to the upper part, i.e. deep-sea ichnofacies, Nereites ichnofacies, andZoophycos ichnofacies. From the vertical evolution of biogenic structures and ichnofacies it could be considered that during the Carboniferious a bathayl basin was gradually changed into a semideep sea basin where progradational sediments in the sea regression were deposited. The Carboniferous represents the sedimentary characteristics during a sea-level falling cycle.